Low-Temperature Clay Mineral Dehydration Contributes to Porewater Dilution in Bering Sea Slope Subseafloor

摘要: Widespread diagenesis of clay minerals occurs in deeply buried marine sediments under high-temperature and high-pressure conditions. For example, the smectite-to-illite (S-I) transformation has been often observed at situ temperatures above ~60°C. However, it remains largely unknown whether such diagenetic processes naturally occur relatively shallow low-temperature and, if so, what consequences are any related chemical reactions to geochemical characteristics deep biosphere. We evaluated possibility occurring S-I below 40°C continental slope Bering Sea by examining porewater chemistry, mineralogy, composition measured ~800 m beneath seafloor (mbsf) core samples acquired during Integrated Ocean Drilling Program Expedition 323. In from these cores, chloride concentrations decreased with increasing depth 560 mM near 500 mbsf; δ18O increased 0‰ 1.5‰; δD –1‰ –9‰. These trends consistent addition water derived transformation. The discrete low Cl– spikes between ~200 mbsf ~450 could be attributed dissociation methane hydrate. X-ray diffraction analysis clay-size fraction (<2 µm) showed an increase illite content I/S mixed layer 150 mbsf. This may imply occurrence decrease Fe3+/Fe2+ strongly suggests microbial reduction Fe(III) burial, which also potential promote Our results significant ecological roles on siliciclastic underlying high-productivity surface seawater margins.